Low molecular weight siloxanes have been known for a long time as vaporizable carriers in cosmetic preparations (T. Koini, M. D. Berthiaume, A. Huber in: SÖFW-Journal, 125th volume 4/99, 22). In particular, octamethylcyclotetrasiloxane could be found widely in cosmetic applications due to its relatively high rate of vaporization and its pleasant feel on the skin (Product Description SF 1173, SF 1202, SF 1204, SF 1246 General Electric (GE) Silicones CDS 4958-E/ENG/0797).
In recent times, doubts have been raised concerning the use of octamethylcyclotetrasiloxane in cosmetic formulations from the points of view of physiological compatibility. In animal experiments, reduced fertility has been observed in cases of extreme dosages. For this reason, efforts have recently increasingly been undertaken to replace octamethylcyclotetrasiloxane in cosmetic formulations with suitable components; these substitutes have hitherto not achieved the performance and properties profile of octamethylcyclotetrasiloxane. Thus, firstly, the rate of vaporization of the decamethylcyclopentasiloxane used as substitute for octamethylcyclotetrasiloxane is significantly lower. Secondly, both the linear octamethyltrisiloxane and also decamethyltetrasiloxane do not convey the silky, non-greasy feel on the skin typical of the cyclic siloxanes.
It has hitherto not been possible to develop vaporizable carrier substances which are sufficiently volatile and at the same time exhibit the good feel on the skin of the cyclic siloxanes and thus make it possible to dispense with the use of octamethylcyclotetrasiloxane (=D4) as vaporizable carrier in the manufacture of cosmetic preparations. Vaporizable carriers are to be understood here as meaning siloxanes which have a boiling point at atmospheric pressure of less than 250° C. and a vaporization behaviour measured in accordance with DIN 53249 similar to that of D4.
EP 0 980 885 describes mixtures of volatile siloxanes which can be used in cosmetic formulations. The objective of EP 980 855 is to seek volatile linear siloxanes which have been only 80-85% by weight vaporized after 30 minutes in accordance with DIN 53249.
These siloxanes should thus vaporize more slowly than octamethylcyclotetrasiloxane (=D4).
WO 98-32418 describes transparent antiperspirant gels which may, inter alia, comprise the vaporizable mixtures of the linear siloxanes of EP 980 855 and additionally cyclosiloxane.
However, it gives no indication that alkylsiloxanes with a volatility comparable to that of D4 are preferred or that such compounds have been recognized therein as a replacement for D4.
In contrast to EP 980 855 and WO 98-32418, it was the object of this invention to develop pure substances which can be used as volatile carrier substance in place of D4 particularly in cosmetic formulations, but also in other cleaning formulations, where the vaporization behaviour should resemble as closely as possible that of octamethylcyclotetrasiloxane, remain liquid over large temperature ranges and whose setting point should in particular be at relatively low temperatures. In this connection, it is advantageous that as a result of using pure individual substances, it is possible to reduce the number of substances present in cosmetic formulations. This minimizes interactions of the various substances with one another, meaning that product safety and quality assurance are decisively improved. That is to say, the preferred formulations are the formulations in which the octamethylcyclotetrasiloxane or linear permethylated siloxanes with comparable vaporization behaviour are replaced exclusively by the linear alkylmethylsiloxanes according to the invention in pure form with a content above 85%.
Moreover, the vaporizable siloxanes according to the invention have no or low “whitening”. This is understood as meaning the phenomenon, described in U.S. Pat. No. 5,922,309, of white residues on the skin or the textile.
Moreover, it was an object of the invention to develop siloxanes with a silky, non-greasy feel on the skin and with vaporization properties which are similar to those of octamethylcyclotetrasiloxane or exceed them. Octamethylcyclotetrasiloxane has a setting point at a relatively high temperature of 4° C., which may lead to problems during transportation, storage and processing of formulations and raw material, depending on climatic conditions. It was therefore also an aim of this invention to develop siloxanes with a more favourable, lower setting point. In addition, it was an object of the invention to develop siloxanes with good compatibility with cosmetic raw materials.